Vehicles having crush zones with one or more energy-absorbing devices therein have significantly improved the safety of transportation.
With attention to FIGS. 1 through 3, there is shown one known energy-absorbing device comprised of a hollow metal tube 10 adapted for progressively folding in a collision. In particular, the tube 10 typically yields under an oscillating load with the formation of successive local buckles 12 along its longitudinal axis 14. This relationship is exemplified by the load-displacement curve 16 shown in FIG. 4.
The load-displacement curve 16 can be generally characterized by three stages, which include an initial response 18, a primary energy-absorption response 20, and a final response 22.
In the initial response 18, the tube 10 is elastically deformed until it receives a peak load 24. Typically, these tubes 10 deform under a sufficiently low peak load 24 for preventing injuries to the vehicle occupants while safely maximizing the crash load transferred to them and also maintaining the structural integrity of the vehicle frame upon which the tubes 10 are mounted.
Thereafter, during the primary energy-absorption response 20, the typical tube 10 is plastically deformed under an oscillating load 26. Each oscillation corresponds to the formation of one complete buckle 12 in the tube 10. The total displacement of the tube 10 and the mean value 28 of the oscillating load 26 typically comprise a substantial portion of the crash energy absorbed by the tube 10. Then, in the final response 22, the tube 10 typically is fully crushed with the load rapidly increasing therein.
As shown in FIG. 4, existing tubes 10 typically deform under a mean load 28 that is substantially lower than the peak load 24, e.g. less than half of the peak load 24. It is understood that a tube 10 crushed under a higher mean load can absorb more crash energy than a tube crushed under a lower mean load.
Furthermore, existing tubes 10 typically have a somewhat long construction with a relatively wide cross-section that is defined by a generally thick wall. In this way, the tubes 10 typically occupy a large space within an end structure of the vehicle.
It would therefore be desirable to provide an energy-absorbing device having an efficiently packaged construction for improving the management of crash energy.